The present invention relates to techniques for effectively coupling a data communication device for a speech or hearing impaired user, such as a TDD or TTY, to a digital wireless telephone unit, to enable communication for the impaired user through a digital wireless telephone network.
Modern society offers people many opportunities and in fact places many demands on people to communicate with each other, often over great distances. One of the most common forms of communication involves conversational speech communicated between two or more parties through a telephone network. Today, such telephone communication is virtually ubiquitous throughout the modern world. A person can simply take a telephone off-hook at one location, dial a destination telephone number, and if someone answers the called telephone, the caller can converse with the other party anywhere in the world.
The communication of speech over the telephone network depends on both parties having good auditory abilities, to speak and hear each other. Persons with hearing and/or speech impairments often can not utilize voice-grade telecommunications services. For many years, these problems barred hearing or speech impaired individuals from communicating via the telephone network.
Data devices transmitting messages in the audio range carried by the telephone network were developed to allow such individuals to communicate through the network. The most common device for this purpose, a telecommunication device for the deaf xe2x80x9cTDDxe2x80x9d or similar device, typically appears as a simple computer or teletype (TTY) terminal. The TDD or TTY utilizes Baudot code to transmit and receive low speed character data. Typically, one user keys in conversational information on one TDD, which sends character data through the telephone network. Another user""s TDD receives and displays the information. These TDD or TTY devices allow individuals having hearing or speech impairments to send and receive communications over any media that can transport the low-speed Baudot code. Many people with speech or hearing impairments and people they communicate with have used TDDs for some years now and have become quite accustomed to use of such devices in their everyday lives.
The Baudot code used by TDDs transmits characters represented by five binary information bits, which means that the character set is limited to 32 characters. To convey more characters, one character is designate xe2x80x9cLTRsxe2x80x9d indicating that subsequent characters represent letters, and another character is designated xe2x80x9cFIGsxe2x80x9d indicating that subsequent characters represent numbers.
The TDD or TTY device originally was designed for communication over analog telephone lines. Such a device sends the ones (1s) and zeros (0s) representing the five-bit binary Baudot character codes as separate audio tones, commonly referred to as xe2x80x9cMARKxe2x80x9d and xe2x80x9cSPACExe2x80x9d tones in a form of frequency shift key (FSK) modulation. The tone frequencies (1400 Hz and 1800 Hz) originally were selected to enable accurate transport thereof through the telephone network. The telephone network itself is optimized to carry a limited portion of the audio spectrum, which normally contains the majority of audible information for human speech, typically in a range of approximately 300-4000 Hz. As such, the data communication devices commonly used by speech or hearing impaired individuals typically send and receive information in the form of FSK MARK and SPACE tones within the narrow audio bandwidth of the analog telephone service.
Use of a TDD/TTY data device enables the hearing impaired to communicate from any location having an analog telephone line to any other location having an analog line connection to a compatible device. As the telephone network has grown, this TDD service based on a telephone line connection has enabled people to use the TDD from almost any fixed location in the world. The main limitation has been that the user must communicate with someone having a compatible device and line connection. People who routinely communicate with hearing or speech impaired individuals have obtained compatible data devices. Many emergency services (e.g. E911), telephone companies, other businesses and government agencies also have installed compatible equipment to allow the impaired individuals to use their TDDs/TTY to communicate with operators/agents or even to interface with automated attendant systems for various purposes.
Modern society, however, also is becoming increasingly mobile. Many new communications services have emerged, to allow people to communicate freely as they roam, without the need for a fixed network connection. As the services have evolved, however, they have created new problems of access for persons with speech or hearing impediments.
To enable communications for people on the go, a number of wireless mobile services have evolved and grown exponentially. Analog cellular telephone service is now quite common throughout much of the developed world and continues to serve many customers. In recent years, a number of digital wireless communications technologies have begun to compete with and gradually replace the analog wireless service. All of these services enable a customer to make and receive wireless, voice-grade telephone calls from virtually any point in the carrier""s service area. With roaming agreements, customer may obtain the mobile service from almost anywhere in a country or continent.
The digital versions of the mobile services offer a number of advantages over the older analog technology, most notably improved performance, much greater security/privacy, alternate communication of data, and easier implementation of new enhanced service features. In view of the advantages, the trend in the industry is to migrate over from the old analog wireless service to the newer digital wireless services.
As noted, the TDDs send and receive analog tone signals to carry the typed textual information. This technique is quite effective over the voice-grade landline telephone network. Users with TDDs and similar TTY devices also have had success communicating over analog cellular telephone networks. However, more modern digital wireless networks do not accurately transport the tone signals. The digitizing and compressing of the audio information and the associated noise reduction processing necessary in a digital wireless network badly distort the FSK MARK and SPACE tone signals used by TDD/TDY devices. This prevents persons wanting to continue to use their TDDs or TTYs from using the more modern digital wireless telephone systems, obtaining the benefits thereof or accessing many of the more modern service features available through the new digital mobile telephone networks.
Today there are many more modern data devices available that provide faster data communications than the TDDs or TTYs. Personal computers (PCs), in particular, offer fast textual data processing and communication in combination with multimedia capabilities. Most digital wireless stations and wireless communication networks support data communication, for example to and from laptop PCs. These communications carry the data over the air interface as digital data, without analog modulation or the need to pass analog signals back and forth through the noise reduction and vocoder circuitry. Such data devices and wireless communications provide far superior communications and increased mobility, and one solution for current users of TDD/TTYs might be to upgrade to these more modern data devices and communication technologies.
However, many people who have used the TDDs or the like for a substantial time are very reluctant to upgrade to the newer data devices. They are familiar with the TDDs and the conversation-like textual communication that those devices provide. They may be uncomfortable with the more complex operations of PCs. Also, anyone communicating with a person with an impairment needs to have a compatible device. Many already have TDD or TTY compatible equipment. An impaired user seeking to upgrade to newer types of data devices would incur the costs of the upgrade and force many people who regularly communicate with the user to upgrade to insure continued compatibility.
Also, for persons with certain impairments, TDD/TTY communication offers a xe2x80x9ctalk-overxe2x80x9d feature that they want to maintain. Many individuals with hearing impairments can speak sufficiently clearly to talk over the telephone, but they can not hear the speech of the other party. A person with a speech impairment often can still hear normal speech. Many modern TDD/TTY devices support communication of voice blended with the MARK and SPACE tones of the TDD/TTY communications. For example, a hearing impaired individual might use a TDD to receive and display text communications from a caller but choose to speak in response. The speech signals are transmitted through the telephone network to the other party who hears the speech in the normal manner. Similarly, a person with a speech impairment needs to send data but can hear spoken responses from a distant party. Many of the newer data communication techniques do not support this combination of voice and data communication for the hearing impaired, and this further discourages replacement of the older TDD/TTY equipment.
It is imperative that all persons have equal access to modern communication services, including persons having hearing or speech impairments. This need for access extends to wireless mobile communications and to the more modern digital networks for such wireless communications. A need therefore exists for a technique to effectively communicate the data signals of the common data devices used by hearing or speech impaired persons, typically TDD or TTY devices, through digital wireless telecommunications networks. It has been suggested that such communications through the digital wireless networks should achieve an error rate of 1% or less, as currently possible through analog networks. There is a more specific need to enable communication of TDD/TTY information together with speech information, through such networks.
The invention addresses the above stated needs by providing effective techniques for converting the tone signals of the data devices to data signals compatible with the air interface of the digital wireless communication network. Over the air-link, the mobile units and base stations communicate the TDD or TTY type information as data messages, without coding of an analog signal in digital form. These data messages, representing the bits of the data, are inserted into the stream with any other information for the particular subscriber, for example, into the stream with any vocoded audio information.
To the person having a TDD or similar device, the digital wireless communication network appears entirely transparent and provides a service virtually identical to an older style analog connection. The protocol conversion bypasses the noise reduction and vocoder circuitry, eliminating the problems of encoding the analog audio tone signals. The multiplexing of the data words with the vocoded audio information allows a person to selectively use both the TDD/TTY data communication and speech communication in one session. The data device for the hearing or speech impaired user operates exactly as it always has and provides the user all of its existing service features. The user, however, may now connect to and take full advantage of the newer digital mobile communication network.
The present invention encompasses methods of providing the inventive access as well as equipment for such access, such as handsets, interfaces, mobile switching centers and wireless networks incorporating the equipment for the necessary protocol conversions.
Certain aspects of the invention relate to methods of providing digital mobile communications for an impaired user. A first such method involves providing digital wireless communication of vocoded audio information between a mobile station and a base station and relaying the audio information over a landline telephone network. At the mobile station, data signals are converted between a tone signal data format, used by a data device for the impaired user, and data messages in a format compatible with digital communication between the mobile station and the base station. The inventive method entails transporting the data messages between the mobile station and the base station together with the vocoded audio information. The mobile switching center provides a conversion between the data messages and tone signal data, in the format for the data device and in a form compatible with transport through the telephone network. The tone signal data is relayed between the mobile switching center and the landline telephone network, together with any audio information.
The communication method may provide digital transport of the data for the impaired user in the forward direction from the network and the mobile switching center toward a terminal coupled to the wireless mobile station. Alternatively, the method may provide transport of the data in the reverse direction, from a terminal coupled to coupled a mobile station through the mobile switching center and the network. Of course, the method also may facilitate two-way communication.
Thus, another method aspect of the invention relates to the processing of the data communication for the impaired user in the forward direction. This method entails receiving analog audio tone signals signifying input data, from a data communication device for the impaired user, and carrying representations of the analog audio tone signals through a telephone network to a digital wireless communication network. In a typical implementation, a telephone network digitizes all audio information and delivers the digital information to the mobile switching center. Any tones are contained in the digital data, for example in pulse code modulated (PCM) form. The digital wireless communication network generates representative data messages in digital form, in response to the representations of the analog audio tone signals. The digital wireless communication network transmits the representative data messages over an air-link to a mobile wireless station. Representative data messages received through the mobile wireless station are converted into corresponding analog audio tone signals, which are supplied to another data communication device for an impaired user coupled to the mobile wireless station.
Another method aspect of the invention relates to the processing of the data communication for the impaired user in the reverse direction. This method entails receiving analog audio tone signals representing input data, from a data communication device for the impaired user. Representative data messages in digital form are generated in response to the analog audio tone signals and transmitted from a mobile wireless station over an air-link to a base station. This method also involves converting representative data messages received through the base station into corresponding signals representing the audio tone signals in a format compatible with a landline telephone network, e.g. as PCM data representing the tone signals. The landline telephone network carries the corresponding signals representing the audio tone signals to another data communication device for an impaired user, which receives and processes the analog audio tone signals.
Other aspects of the invention relate to equipment for implementing the wireless communications for the impaired user, such as a digital wireless telephone network, a mobile switching center for use in such a network and a handset or interface to a handset specifically adapted to couple to the user""s device and provide the appropriate conversions.
For examples a mobile user""s apparatus might include a vocoder, a digital transceiver, a tone detector and a processor. The vocoder digitally encodes analog audio signals to form vocoded speech samples and decodes vocoded speech samples into analog audio signals. The digital transceiver provides two-way wireless communication of vocoded speech samples to and from the vocoder. The tone detector senses analog tones representing data from the data device for an impaired user. The processor generates digital data messages corresponding to the sensed analog tones. The processor supplies the data messages to the digital transceiver, for over-the-air transmission with vocoded speech samples from the vocoder.
The elements of this apparatus for the mobile user may be incorporated into a wireless mobile station. Alternatively, the wireless mobile station may include the vocoder and transceiver, and a separate interface connected to the station contains the tone detector and the processor.
The preferred embodiment of the user""s apparatus also includes elements for receiving data for the impaired user. Specifically, the apparatus further comprises an analog tone generator, coupled to the processor, for generating analog tones representing data for the data device for the impaired user. The processor instructs the tone generator to generate the analog tones upon receipt of digital data messages corresponding to analog tones through the transceiver.
The mobile switching center used with the invention includes a digital switch for establishing selective connections to circuits going to digital wireless base stations. A demultiplexer, coupled to the digital switch receives a user""s digital data stream, received from a mobile unit through one of the wireless base stations. From this digital stream, the demultiplexer separates digital messages representing predetermined tone signals for the data device for the impaired user from vocoded speech samples. The switching center also includes a vocoder coupled to the demultiplexer. The vocoder digitally decodes the speech samples into representations of analog audio signals, e.g. in PCM form. A decoder, coupled to the demultiplexer, decodes the digital messages to identify the predetermined tones. The mobile switching center includes a generator that produces representations of the predetermined tones in response to instructions from the decoder. A combiner combines the representations of analog audio signals and the representations of the predetermined tones into a signal stream for transmission over a telephone network.
In the preferred embodiment, the switching center also processes signals bound for the impaired mobile user. Specifically, the switching center further comprises a tone detector and an encoder. The tone detector recognizes representations of predetermined tone signals for the data device for the impaired user, typically in signals received through the telephone network. The encoder generates digital data messages corresponding to the detected tone signals, for transmission through the base station and the air-link to the user""s wireless mobile station.
Additional objects, advantages and novel features of the invention will be set forth in part in the description which follows, and in part will become apparent to those skilled in the art upon examination of the following or may be learned by practice of the invention. The objects and advantages of the invention may be realized and attained by means of the instrumentalities and combinations particularly pointed out in the appended claims.